Tiffany visits Lucas at his apartment in order to gather the rest of her belongings the day after his incident at the diner, when Lucas is still shaken and confused about what has happened. During her stay, Lucas can choose to act towards her in certain ways (aggressively, sad, brave, etc.) and depending on the choices of the player, Lucas can either fail in trying to kiss her resulting in her leaving, or play his guitar for her resulting in them sleeping together (if the player succeeds in the guitar-playing quick time event).
Whether Tiffany leaves or stays for the night has a major impact on Lucas' mental state, which will either improve or suffer a tremendous setback, which may even drive him to suicide, if it drops to zero.
Later, Tiffany is kidnapped by The Oracle from the Orange Clan in order to draw Lucas out in the open. She is tied up at the top of a rollercoaster in an abandoned amusement park, but when Lucas comes to rescue her, they are both ambushed and killed. Lucas is resurrected by Agatha, but Tiffany remains dead, and Lucas is later seen visiting her grave, where he allows Carla Valenti to come meet him, because he does not want to run or hide anymore.
If Lucas succeeds in getting Tiffany to stay the night, the couple end up having sex in his bed, and the player control Lucas' 'thrusts' via the mouse ( PC) or joystick (consoles). This scene was edited out of the North American release of the game (titled Indigo Prophecy - the international version was called Fahrenheit), in order to avoid earning the game an 'Adults Only' rating.